The objective of this project is to establish the maximum duration of cerebral tolerance of ischemic anoxia, to evaluate the association of ischemia and hemorrhage in primate models and to determine the maximum time allowable to begin therapeutic intervention by a number of methods. Having established the pathologic anatomy of models of ischemia, acute experiments using hydrogen washout blood flow methods, EEG, oxygen polarography, the early stages of evolution of ischemia have been studied. These parameters will be monitored simultaneously in both primary and secondary zones of disordered circulation before, during and after a) embolectomy and b) middle cerebral-temporal artery anastomoses in dogs. Models have been developed for segmental cerebral artery occlusion in dogs and primates. Hemorrhagic or bland infarction can be selectively produced depending upon the duration of ischemia prior to reflow through vessels in the ischemic field. Using hemorrhagic infarction as the marker of excessive time lapse, the salutory and pejorative effects of microvascular surgery will be tested under a) N2O and b) pentobarbital anesthesia.